Nonwoven fabrics of improved opacity



Sept 1, 1970 N. s. NEWMAN 3,526,526

NONWOVEN FABRICS OF IMPROVED OPACITY Filed Oct. 20, 1967 3,526,526NONWOVEN FABRICS F IMPROVED OPACITY Nicholas S. Newman, West Newton,Mass, assignor to The Kendall Company, Boston, Mass., a corporation ofMassachusetts Filed Oct. 20, 1967, Ser. No. 676,955 Int. Cl. 1344c 1/08US. Cl. 117-25 13 Claims ABSTRACT OF THE DISCLOSURE The opacity andlight-scattering power of nonwoven fabrics is increased by adhesivelybonding to the fabric surface between 200* and 1,000 aggregates ofultra-short fibers per square inch. The ultra-short fibers are between40 and 200 microns in length, and the aggregates are randomlydistributed on a planar fabric, or concentrated at the raised surfaceportions of a non-planar fabric.

This invention relates to the preparation of bonded nonwoven fabrics ofenhanced surface appeal. More particularly it relates to the preparationof a bonded web of unspun and unwoven textile-length fibers, at leastone surface of which is characterized by having adherent thereto amultiplicity of irregularly spaced aggregates of ultra-short, nontextile-length fibers.

Bonded nonwoven fabrics, comprising dry-assembled textile-length unspunand unwoven fibers bonded by polymeric binding materials, are produced'by a variety of well-known processes and are a staple article ofcommerce. In additional numerous industrial applications, they arefinding increasing use in such fields as disposable or limited usegarments, sheets, pillowcases, draperies, and the like. Conventionalnonwoven fabrics, however, are substantially planar and uniform, devoidof the surface interest associated with woven fabrics which have yarninterlacings which interrupt the surface in a regular or irregularmanner.

Additionally, nonwoven fabrics of a weight range which may economicallybe used as disposable items are translucent, even highly so, and lackthe concealing power which is generally desired.

Attempts have been made to overcome this lack of surface interest byprinting a pattern or design on the surface of nonwoven fabrics, or byembossing the surface by means of patterned pressure rolls. Suchexpedients are expensive, and are generally ineffective in increasingthe opacity of a nonwoven fabric. It has also been proposed to flock thesurface of nonwoven fabrics, by the mechanical or electrostaticdeposition of fibers out to 1 to 8 millimeters (LOGO-3,000 microns) inlength onto a nonwoven fabric which has been provided with an adhesivecoating. In conventional flocking, individual cut fibers are orientedsubstantially perpendicularly to the plane of a nonwoven fabric. Such aprocedure does increase the opacity of nonwoven fabrics, but the surfacetexture developed is that characteristic of a suede 0r velvet, and notlike a conventional woven fabric. Moreover, precision-cut flock isgenerally more expensive than the textile filaments from which it isderived.

It has now been found that a pronounced delustering and opacifyingfinish can be added to nonwoven fabrics if ultra-short fibers, of from40 to 200 microns in length, are deposited on an adhesive-coatednonwoven fabric in the form of numerous and irregularly distributedfibrous aggregates, said aggregates having an average diameter of 4 to10 times the average individual fiber length and preferably numbering200 to 1,000 aggregates per square inch of fabric surface. Such a finishnot only decreases the transmission of light through the fabric, but itgreatly United States Patent 0 increases the random scattering ofincident light. Since the ultra-short fibers are low in cost compared tocut flock, their use in the process of this invention provides aneconomical enhancement of nonwoven fabrics which renders them moresuitable for disposable items where the simulation of a woven fabric isdesired.

It is therefore an object of this invention to provide a low costnonwoven fabric which simulates the surface reflectance properties ofwoven fabrics. It is also an object of this invention to provide afinish for a nonwoven fabric which increases its opacity and maskingpower without decreasing its porosity, drape, and flexibility. Otherobjects of the invention will be apparent from the following descriptionand drawings, in which:

FIG. 1 represents a plan view of the surface of a typical nonwovenfabric of this invention, highly magnified.

FIG. 2 is a similar view of another embodiment of the invention.

FIG. 3 is a schematic representation of an apparatus suitable forcarrying out the process of this invention.

In FIG. 1, a conventional nonwoven fabric 10 is shown as beingsurface-textured by aggregates of ultrashort fibers 12, said aggregatesbeing irregularly distributed over the surface of the fabric. In theprocess of the invention there is a certain amount of individual fiberfall-out 14, where non-aggregated fibers are adhesively bonded to thefabric surface, but it is desirable that a substantial proportion (50%or more) of the ultra-short fibers be agglomerated in the form ofaggregates distributed randomly over the surface of the product.

As base material a wide variety of nonwoven fabrics may be used, bondedby a variety of processes well known in the art.

In general, in the field of disposable articles where cost is a primaryconsideration, the nonwoven fabrics will weight from 15 to 40 grams persquare yard, will be composed of cotton or rayon, and will be bonded bysaturation with a polymeric latex binder which imparts tensile strengthand toughness adequate for the desired end use. The nonwoven fabric may,if desired, be reinforced with a scrim or open-meshed woven fabric. Theselection of such fibers and binders is well known to those skilled inthe art, and forms no part of the present invention.

It is also possible to utilize as starting material a very lightlybonded or even an unbonded web, as disclosed in my copending applicationSer. No. 444,536, filed Apr. 1, 1965. In such cases, the tensilestrength of the fibrous base may not be sufficient to withstand thesaturation step disclosed in FIG. 3, and recourse is had to spraying theweb with binder, or saturating it while it is supported between twoscreens, as is understood in the art.

As ultra-short fibers it has been found that a length of between 40 and200 microns, in the case of cellulosic fibers, is a desirable range forthe promotion of fibrous aggregates. Regular commercial flock, ofLOGO-8,000 microns in length, does not form coherent aggregates, buttends to be dposited in the form of individual fibers orientedperpendicularly to the fabric surface. This is true whether theflock-deposition process is mechanical or electrostatic, or acombination of both. The result is a smooth and uniform pile-likesurface, as set forth above. The clumping which gives the characteristicfrosted and irregularly-reflective surface appearance desired in theproducts of this invention appears to be related to fiber length, forreasons which are not entirely understood. It may be that as the lengthof a fibrous particle begins to approach its diameter, the lesseffectively are the particles oriented perpendicularly to the nonwovenfabric surface, particularly in the case of electrostatic flocking.

For reasons of economy, it is preferred to use ultra- 3 short cellulosicfibers, such as ground (and preferably bleached) wood pulp or groundcotton. Other ultra-short fibers may be used provided that they tend toagglomerate in a flocking operation rather than disperse into a uniform, pile-like distribution.

The application of such ultra-short fibered aggregates to a nonwovenfabric may be effected conveniently by a flocking range of conventionaldesign, shown schematically in FIG. 3. A supply roll 20 of nonwovenfabric is provided with a polymeric latex coating, either by asaturation and squeeze as shown at 22, or by spraying, or by knife orroller coating or similar means. The ultrashort fibered aggregates areapplied at stage 24, where the aggregates are deposited on theadhesively-coated nonwoven fabric from a screen 26. Beater bars 28assist in the distribution and anchorage of the aggregates, and theprocess may optionally be coupled with the driving power ofelectrostatic forces as is well known in the art. A vacuum source 30removes a considerable part of the excess unanchored ultra-short fiberedaggregates, after which the assembly is dried at stage 32. This may becarried out by a heated oven, steam cans, infrared lamps, and the like.A brushing stage 34, to remove final traces of unanchored aggregates, isfollowed by a windup 36.

Particularly interesting results are obtained when the nonwoven fabricbase contains a layer of scrim or is otherwise reinforced with yarns orpseudo-yarns, or is embossed or locally deformed to cause a patternedprotrusion on the nonwoven fabric surface. Such a structure is shown inFIG. 2, where a base nonwoven fabric 11 has been reinforced, during itsmanufacture, with an openmeshed scrim comprising warp yarns 16 andfilling yarns 18. There is a minor amount of individual ultra-shortfibrous coverage 14, but the preponderance of the fibers are in the formof aggregates 12 which are concentrated chiefly along the yarn-likepattern which protrudes from the surface of the fabric. The reason for adisproportionate number of aggregates being found distributed in ascrim-like pattern may lie in the fact that those areas immediatelyoverlying the yarns have a higher capillarity, and higher adhesiveconcentration, than the balance of the nonwoven fabric. Or the reasonmay be a purely physical one, since it is known that especially whenelectrostatic forces are used, a charged particle tends to travel theshortest path and to direct its course to the highest points on theoppositelycharged surface to which it is attracted.

The process of this invention offers an economical and expedient methodfor increasing the opacity of nonwoven fabrics, for increasing thelight-scattering characteristics of the surface of the fabric, and forincreasing the weight and absorbency of the fabric without the sacrificein softness and flexibility associated with processes which increase theweight by adding more textile-length fibers. It will be illustrated bythe following example.

EXAMPLE I A bonded nonwoven fabric of 74% rayon, 13% nylon, and 13%acetate fibers, all of textile length, was prepared by carding a blendof said fibers into a fleece weighing 26 grams per square yard. Thisfleece was saturated with an acrylic binder in latex form to add 21grams of dry binder to each square yard of material after drying.

Using the process illustrated in FIG. 3, this bonded fabric wassaturated with an adhesive acrylic latex polymer, and ultra-shortcellulosic fibers were deposited thereon in a mechanical flockingoperation using beater bars and without the aid of electrostatic forces.The ultra-short fibers were Solka-Floc BW-200, a trademarked fiber ofthe Brown Paper Company. After drying and brushing the product weighed65 grams per square yard and had bound thereto 15% of ultra-shortfibers, principally in the form of fibrous aggregates distributedrandomly over the surface, which resembled FIG. 1. The product reflectedlight in an irregularly scattered fashion appearing opaque and delustredin comparison with the base fabric. The machine direction tensilestrength had increased over the base fabric by 27%; thecross-directional strength by and the cross-directional tear resistanceby 58%.

An embodiment of this invention in which the process is carried out onan unbonded web or fleece is illustrated by Example II.

EXAMPLE II An unbonded assembly was prepared consisting of two cardedwebs, each 7 grams per square yard, of 1.5 denier 1%, inch rayon fibers,separated by a layer of 8 x 8 scrim weighing 10 grams per square yard.

Using a double-screen saturating process, this assembly was saturatedwith about 250% of a 25% solution of an adhesive acrylic polymer, andthe same ultra-short cellulosic fibers as in Example I were deposited ina mechanical flocking operation using beater bars and without the aid ofelectrostatic forces. After drying and brushing the product weighed 55grams per square yard and contained 30% flock adherent to its surfaceprincipally in the form of fibrous aggregates as illustrated in FIG. 2,with a preponderance of the aggregates distributed along lines definedby the yarns in the layer of scrim. The product had a pleasinglyirregular or frosted surface appearance.

A similar nonwoven fabric base was prepared using the same type ofscrim, but increasing the weight of the rayon webs so that the finalbonded fabric weighed the same as the fabric above, 55 grams, butwithout the addition of ultra-short fibrous aggregates. The surfaceappearance of this plain fabric was planar, lacking in interest, andwithout the diffusing effect on incident light displayed by the fabricof Example I.

The flexibility of the two fabrics was measured by the cantileverprinciple based on the Fabrics Research Laboratory Tester (FederalSpecification CCC-T-191b). In this test, rigidity is expressed incentimeters, lower readings indicating greater softness or drape.

Rigidity in centimeters Machine direction Cross direction Example I 2. 43. 6 Plain fabric 8. 3 4. 4

fabric of equal weight.

Having thus described by invention, I claim:

1. The process for enhancing the surface of a nonwoven fibrous assemblywhich comprises applying a coating of adhesive to at least one surfaceof the assembly,

applying to the coated surface in random distribution a plurality ofaggregates of ultra-short fibers,

said ultra-short fibers being between 40 and 200 microns in length,

the average diameter of the fibrous aggregates being between 4 and 10times the average fiber length, and drying said fibrous assembly.

2. The process according to claim 1 in which the fibrous assembly is abonded nonwoven fabric.

3. The process according to claim 1 wherein between 200 and 1,000fibrous aggregates are applied to each square inch of surface of theassembly.

4. The process according to claim 1 in which the ultrashort fibers arecellulosic.

5. The process for enhancing the surface of a yarnreinforced nonwovenfibrous assembly which comprises applying a coating of adhesive to atleast one face of a fibrous assembly which comprises yarns which 6 causea protruding pattern on the face of the as- 11. A nonwoven fabric ofenhanced opacity, flexibility, sembly, and surface texture whichcomprises applying to the coated surface a plurality of aggregates abase layer of nonwoven fabric with a protruding pat of ultra-shortfibers, tern on at least one face of said fabric,

said ultra-short fibers being between 40 and 200 microns 5 to which faceis adhesively united a plurality of agin length, gregates of ultra-shortfibers,

the average diameter of the fibrous aggregates being said aggregatesbeing predominately concentrated on betWeen 4 and 10 times the averagefiber g and in the immediate vicinity of said protruding and drying saidfibrous assembly, pattern,

whereby a preponderan e of Said fi r ll aggr gates 10 the fiberscomprising said aggregates being between 40 are caused to adhere to thefibrous assembly on and d 200 microns in length, in the immediateVicinity of the protruding Pattern the average diameter of the fibrousaggregates being caused by the yarns. between 4 and 10 times the averagefiber length.

The Process according to Claim 5 wherein between 12. The productaccording to claim 11 wherein there 200 and 1,000 fibrous aggregates arepp 10 each 15 are between 200 and 1,000 fibrous aggregates per squaresquare inch of surface of the fibrous assembly. i h f nonwoven fabrisurface,

The PrOeeSS according to Claim 5 in which the ultra- 13. The productaccording to claim 11 wherein the short fibers are cellul si ultra-shortfibers are cellulosic.

8. A nonwoven fabric of enhanced opacity, flexibility, and surfacetexture which comprises References Cited a base layer of nonwovenfabric,

TES PAT NTS to at least one face of which is adhesively united a UNITEDSTA E 3 X plurality of aggregates of ultra-short fibers, 3,356,52112/1967 e g 117 3 said aggregates being distributed over said surface,3,434,858 3/1969 Dlckmson 117 33 X the fibers comprising said aggregatesbeing between 40 3,459,579 8/1969 Newman 117-33 and 200 microns inlength, the average diameter of the fibrous aggregates being WILLIAMMARTIN Pnmary Exammer between 4 and 10 times the average fiber length.P. ATTAGUILE, Assistant Examiner 9. The product according to claim 8wherein there are between 200 and 1,000 fibrous aggregates per squareinch US. Cl. X.R. of nonwoven fabric surface. 117-33; 161-64 10. Theproduct according to claim 8 in which the ultra-short fibers arecellulosic.

